This invention is related to a device for cleaning interior surfaces of a heat exchanger device, and more particularly, to a sootblower for use with combustion air pre-heaters associated with large scale utility or industrial boilers.
Sootblowers are used to project a stream of a blowing medium, such as steam, air, or water against heat exchange surfaces of large-scale combustion devices, such as utility boilers. In operation, combustion products cause slag and ash encrustation to build on heat transfer surfaces, degrading thermal performance of the system. Sootblowers are periodically operated to clean the surfaces to restore desired operational characteristics.
Generally, sootblowers include a lance tube that is connected to a pressurized source of blowing medium. The sootblowers also include at least one nozzle from which the blowing medium is discharged in a stream or jet. In a retractable sootblower, the lance tube is periodically advanced into and retracted from the interior of the boiler as the blowing medium is discharged from the nozzles. In a stationary sootblower, the lance tube is fixed in position within the heat exchanger and is periodically rotated while the blowing medium is discharged from the nozzles. In either type, the impact of the discharged blowing medium with the deposits accumulated on the heat exchange surfaces produces both a thermal and mechanical shock that dislodges the deposits. U.S. Pat. Nos. generally disclosing sootblowers include the following, which are hereby incorporated by reference: 3,439,376; 3,585,673; 3,782,336; and 4,422,882.
A typical sootblower lance tube comprises at least two nozzles that are diametrically oriented to discharge streams in directions 180xc2x0 from one another. Various cleaning mediums are used in sootblowers. Steam and air are used in many applications. Cleaning of slag and ash encrustations within the internal surfaces of a combustion device occurs through a combination of mechanical and thermal shock caused by the impact of the cleaning medium. In order to maximize this effect, lance tubes and nozzles have been designed to produce a coherent stream of cleaning medium having a high peak impact pressure.
In some sootblowing applications, there is a need to periodically change the cleaning media being used in response to changing cleaning requirements within the combustion device or due to the collection of deposits arising from the injection of flue gas treatment chemicals, such as ammonia. Specifically, there is a desire to alternatively use steam or water as a cleaning media. Water and steam have significant operational differences as cleaning media. Steam is the most typical sootblowing media and is used since it is highly effective and can be used over a long-term period without damaging internal surfaces of the heat exchanger elements being cleaned. In some very demanding fouling conditions, steam does not provide the level of cleaning effect necessary. Due to a greater mechanical effect, water is capable of cleaning the most severely fouled surfaces. Water also dissolves salt deposits, such as ammonia bi-sulfate. However, in some applications, continuous use of water is not desired due to a fear of damage to the internal heat transfer components over repeated cycles. Various approaches toward providing dual media sootblowing capabilities have been developed in the past. In one approach, a change of the cleaning media would involve a complete change of the sootblower lance tube, with one having nozzles intended for one type of cleaning media, and another lance tube having nozzles intended for a different type of cleaning media. Specifically, one lance tube would have nozzles adapted for water, and the other lance tube would have nozzles adapted for steam. Due to the different fluid characteristics of water and steam, the water discharge nozzles are considerably smaller in diameter than steam nozzles. Designs of lance tubes having interchangeable nozzles have been considered, but are problematic since the lance tube operates in a hostile environment, and therefore, threads or other precision mating surfaces tend to become degraded in service, making removal and replacement of specialized nozzles difficult.
In the previously described approaches, the task of changing cleaning media is a significant and time-consuming and labor-intensive effort that takes the cleaning equipment out of service for a significant time period. Several other approaches that do not necessitate a complete change In lance tube or nozzles have also been considered. One example is described by U.S. Pat. No. 5,509,607 assigned to the Assignee of this invention and which is hereby incorporated by reference. That patent describes a lance tube having two sets of nozzles with a water discharge nozzle being located upstream along the lance tube, and the steam nozzle at the downstream distal end position on the lance tube. A switch in cleaning media is achieved through the use of a valve positioned between the two sets of nozzles. The patent describes a flow passageway that can either be filled with a plug that substantially blocks the flow of fluid to the downstream nozzle or an open passageway allowing free flow of fluid to the distal end. Where it is desired to discharge water, the valve is in the blocking position and pressurized water is supplied to the lance tube that is ejected from the smaller diameter upstream water discharge nozzles. A leakage flow of water is allowed to escape to the distal end of the lance tube for cooling purposes. When it is desired to discharge steam, the valve is set to provide an open flow passage, thus allowing steam supplied to the lance tube to reach the steam discharge nozzles at the distal end. The disadvantage of this approach is that a significant effort is necessary to change sootblowing media.
Yet another approach for dual media disclosure is described by U.S. Pat. No. 4,209,028 which is also assigned to the Assignee of this invention and is hereby incorporated by reference. This patent describes a sootblower lance tube having two sets of nozzles with one set being optimized for water discharge and the other for steam discharge. A thermostatically actuated valve system is employed to direct the flow of fluid to the two sets of nozzles. The theory of operation of the device is based on the fact that the supplied water is cooler than steam and thus a thermostatically sensitive element can be used to exploit this difference and actuate a valving system. This approach has not enjoyed widespread implementation in industry. This is likely attributable to the mechanical complexity of the system which must operate in a very hostile environment within the combustion device.
One common shortcoming of each of the approaches mentioned previously is their inability to allow the simultaneous discharge of two different types of cleaning media, such as steam and water.
In view of the foregoing, there is a need for a sootblower device which is readily adapted for discharging two types of cleaning media, where the change over from discharging one media to the other media can be made with minimal downtime of the sootblower device, and is made with mechanisms that will withstand the hot and corrosive environment experienced in the interior of a combustion device. Moreover, there is a need for such a device capable of simultaneous discharge of two types of cleaning media.